1. Field of the Invention
The present invention relates to engine ignition and charging/regulating systems, such as for gasoline engines with system batteries and associated vehicle electrical systems. More particularly, the present invention relates to marine engine ignition and charging/regulating systems.
2. Description of the Prior Art
It is known in vehicle electrical systems, including marine electrical systems, to generate electricity via alternator coils arranged in a stator assembly associated with a rotor driven by an engine. The rotor moves permanent magnets past pole faces of the stator having alternator coils, thereon, and the alternator coils generate a voltage output which varies with RPM. At low RPM, the voltage is relatively low, and at higher RPMs, the voltage increases.
The output of the alternator coils is connected to a system battery via a charging circuit also functioning to regulate voltage delivered to the system battery and vehicle electrical system connected in parallel to the system battery.
If the system battery, which is typically 12 volts, requires charging as indicated by a low voltage output at the battery, then the charging circuit applies voltage to the battery which is higher than the system battery static voltage so that current will flow into the battery and charge the same. Furthermore, the charging circuit also provides a regulating function relative to the battery and vehicle electrical system such that as the alternator coil voltage output increases above the nominal system voltage with increasing engine and associated rotor RPM, then the charging and regulating circuit maintains the output voltage at 14 volts, for example.
Such prior art charging and regulating circuits typically have been of two types. In a first type known as the "crowbar" or "shunt regulation systems", series connected back-to-back control devices such as SCRs with diodes in parallel thereto are connected parallel to or in shunt with the output of the alternator. At low RPM, the voltage output from the alternator coils is low (for example less than 12 volts), and the shunt control device path is off or open. As the engine RPM increases and the voltage rises, the shunt path begins to turn on such that additional current is drawn. Since the alternator coil winding is typically current limiting by nature, by drawing additional current through the alternator coils, the voltage output can be controlled, and is thus maintained at a given value such as 14 volts, for example. Thus, the 12 volt battery can be charged and the system voltage can be regulated.
At higher RPMs, as the no load voltage from the alternator rises, such as to 120 volts, for example, the shunt current path draws greater amounts of current. Accordingly, high power switching units such as high power SCRs and associated diodes are required. Substantial power is lost through heat dissipation and the cost of such a shunt system is high in view of the high power requirements of the shunt path components and heatsink requirements. For these reasons, it has been known in the prior art to alternatively employ what is known as a "full wave regulating system".
The second type is known as the full wave regulating system, which can be either a full wave center tab type or bridge rectifier type, for example. These circuits employ control devices connected in series with output end of the alternator coil in the manner of a full wave rectifying system. For example, an SCR can be connected in series at each end of the alternator coil. These SCRs have their gates self biased through voltage output sensing with a resistance of the alternator coil relative to the system battery voltage. Initially, the SCRs are turned off at low RPM, since the alternator coil output is, for example, 9 volts whereas the battery voltage is higher, namely 12 volts. When the alternator coil outputs a voltage above the battery voltage by an amount sufficient to create a bias voltage to turn on the SCR, then the SCR connects through at least a portion of the cycle of the alternator voltage to charge the battery. The upper limit of the system voltage is regulated by appropriate switching of the SCR such that as the alternator open circuit voltage rises to, for example 120 volts, the SCR is switched such that only a portion of the voltage waveform is fed through and the system voltage is thus regulated to 14 volts, for example.
Although this full wave prior art system does not have the control device power dissipation problems associated with the shunt regulating systems (since the control devices are in series rather than shunt), there are other disadvantages. At low RPM, the series connected control devices cannot turn on in view of SCR gate biasing problems caused by the need to choose a sensing resistance which does not result in excessive power loss at high voltage - high RPM alternator outputs. Thus the battery is not charged and the vehicle system is draining the battery at low RPMs. Since the sensing resistance in the gate control bias circuit of the SCRs must be chosen to have a relatively small resistance so that the SCRs will turn on as soon as practical at low engine RPMs, at high engine RPMs the dissipation of the resistor is significant in view of the increased voltage drop thereacross. Thus, not only does the system not charge the battery at relatively low RPMs, but also at high RPMs the biasing circuit resistance dissipates substantial amounts of power. Furthermore, resistors capable of dissipating such higher powers are costly.